Marine Mammals

Current Questions in Marine Mammal Research

1. Population Studies

What have we learned from long-term studies of wild dolphins?

Although marine mammal researchers do design experiments to test their hypotheses, much of what they learn is by observing these animals over long periods of time. Since 1970, Dr. Randall Wells of the Mote Marine Laboratory and his colleagues have studied generations of wild bottlenose dolphins around Sarasota, Florida. They have provided valuable information on group behavior and mother-child bonding in wild populations. They have identified 3 main groupings, or pods,of dolphins:

Mothers and juveniles

Young dolphins typically stay with their mothers for several years, three to six years or even longer. Even after they leave their mother's pod, they may return for a visit, and daughters often return when they have their first child.

Bands of juveniles

Generally these pods consist of young dolphins between the ages of three and thirteen. Here, two males may often form strong bonds that may last 10 to 15 years or longer.

Adult males

These male dolphins travel from one pod to another, staying for short periods of time and then moving on.

Dr. Wells and his associates have conducted many populations studies including identification of individual dolphins, evaluations of the health of wild dolphins, mating behaviors, use of echolocation in dolphin feeding behavior, and effects of disturbance by boats on wild dolphins.

By conducting long-term studies, scientists have:

established that that there are pods of coastal dolphins that have lived year-round in the same area for many generations. The National Marine Fisheries Service, which is charged with protecting marine mammals, can use these data to set up protected areas in their home ranges;

provided information on ideal social groupings for captive dolphins; and

provided information about the long-term health effects of environmental pollution. (Usualy, scientists must extrapolate impacts of pollution after the fact from analyzing the corpses of stranded marine mammals.)

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2. Animal Behavior

Do dolphins and whales play?

Dolphins play a lot, especially young dolphins. They spend many hours a day balancing objects such as stones, seaweed, and fish parts on their snouts and flippers, herding fish, and pushing objects with their snouts. It is common to see youngsters in the juvenile pods chasing each other, nipping at each other's fins, finding and sharing objects, and even blowing bubbles (see link). Scientists believe that play behavior teaches the young dolphins the skills they will need to socialize, hunt, mate, and survive as adults. Even as adults, dolphins never seem to lose their interest in playing.

The largest members of the dolphin family, killer whales (orcas), also have been observed at play--playing with their food! Ingrid Visser, a student at the University of Auckland, watched as 19 orcas pursued 55 stingrays. Plowing into them from below, the orcas tossed the stingrays up into the air and batted to other orcas like Frisbees. She theorized that maybe the orcas were trying to stun the stingrays so they wouldn't sting when they swallowed them.

(source: "Playing with their food?" National Wildlife,Feb/March, 1998)

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3. Communications / Echolocation

How do dolphins communicate?

Dolphins make a wide array of sounds, including clicks, moans, chirps,creaks, barks, squeaks, yaps, mews, and whistles. They are also excellent mimics and have been known to makes sounds resembling the engine of a motorboat, the laugh of their trainer, and the brrrr of a Bronx cheer!

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Dolphins use clicking noises in echolocation, which bounce off objects underwater. This allows them to navigate, identify prey and friends, and avoid obstacles and predators. Dolphins use whistles to maintain contact within their pod or when meeting other pods of dolphins. Their whistles may signal danger, a call for help, or simply identification. Scientists think that each dolphin has its own signature whistle, sort of like our names. Whistles may also help dolphins hunt cooperatively and coordinate migratory movements.

Do dolphins have their own language?

For many years, people have been trying to understand if the rich variety of sounds produced by dolphins could be a coded, secret "language." Louis Hermann of the University of Hawaii's Kewalo Basin Marine Mammal Lab is a leader in the field of animal-language research. He does not believe dolphins have their own language, but he has been able to teach artificial language to four dolphins at his lab. He uses two approaches: sight and sound. With one dolphin he uses hand signals to give instructions to fetch a ball or play Simon Says. With another, he communicates using different tones of electronic whistles.

Learn more at the University of Hawaii's Dolphin Institute (formerly known as Kewalo Basin Marine Mammal Lab)

How do scientists study marine mammals' use of sound in social interactions?

Sounds carry a long distance underwater, but we humans, at least, have a hard time pinpointing where the sounds originate. Scientists recording the sounds of captive dolphins often found it impossible to decipher which animals was making which sounds, since marine mammals do not move their mouths when they vocalize.

Peter Tyack, a whale researcher at the Woods Hole Oceanographic Institution, has developed the "datalogger," a computerized instrument designed to record sounds made by captive marine mammals, such as beluga whales and dolphins. Each datalogger contains an underwater microphone linked to a small computer to store information. A datalogger is attached to a subject's back by two suction cups. As the animals vocalize, the datalogger on each animal picks up the loudest sound, revealing who is "talking."

Cheri Reechia, a graduate student at the Woods Hole Oceanographic Institution, is using the data logger to study vocalizations and social behavior among groups of beluga whales at four aquariums. Belugas long ago were nicknamed the "canaries of the sea" because sailors could hear their plaintive calls even through the wooden hulls of their sailing ships.

She believes understanding their vocal and social behavior will be helpful for captive-animal husbandry, perhaps providing information on changing social dynamics, breeding conditions, or the general health of captive belugas. Long-term, she hopes to use dataloggers to study wild beluga society, to track their movements and provide data for their protection in the ocean.

Do whales use echolocation all the time?

Whales and dolphins echolocate-emit clicking sounds that bounce off prey or objects in order to locate and identify them. Some scientists think that captive whales and dolphins do this much more than wild populations. Although all whales chatter up a storm to keep in contact with each other and to communicate (what, scientists don't know), some whales may not use echolocation at all, but may find their prey simply by listening. The fact that sperm whales and right whales are struck by boats suggests they may not be using echolocation to avoid these large objects. Dolphins, too, may turn off their echolocation while traveling, which would explain why they become entangled in drift nets instead of leaping over them.

Scientists have determined that whales stay in touch with each other using a variety of vocalizations. Killer whales make plaintive, wailing noises. Fin whale pods typically have one whale that dominates the conversation while others take turns answering, according to Mark A. McDonald and colleagues at Scripps Institution of Oceanography. Blue whales, they found, call for 20 seconds, pause for 20 seconds, and then repeat the 20-second call.

As underwater noise pollution increases from boat engines, submarines, and oceanographic experiments, researchers feel it is critical to learn more about the way whales use sound in the wild in order to prevent human activities from disrupting the lives of cetaceans.

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4. Physyiology / Adaptations

How do deep-diving whales and dolphins avoid "the bends?

The US Navy would like to know how dolphins and whales avoid a problem that plagues human divers who try to return to the surface too quickly - "the bends." When a human dives, the increasing pressure as he or she descends forces nitrogen from the air supply in the scuba tank into the bloodstream. If the diver tries to ascend too quickly, the nitrogen changes to bubbles in the blood, which can break and cause terrible cramps or even death.

Ocean-going dolphins routinely dive to 200-300 feet. When a dolphin dives past 230 feet (70 meters), its lungs and rib cage partially collapse. This keeps air from passing into the lungs into the rest of the body, so nitrogen cannot dissolve in its blood. The dolphin is compressed into a small, dense shape by the surrounding pressure, causing it to fall like a rock, according to Navy researcher Terrie Williams. Since the dolphin is not using any energy to descend, she says, it doesn't burn up oxygen stored in its blood and muscles. This allows it to hold its breath for as long as five to eight minutes at a time.

How is a whale like a hippo?

Scientists agree that dolphins and whales descended from land animals that were ungulates (like horses, cows, hippos, and camels.) Now some researchers are finding some striking similarities between hippos, which spend much of their time partially submerged in muddy pools, and dolphins, which spend most of their lives submerged in the ocean.

Both may give off underwater sounds through fatty areas in their heads. The dolphin transmits sounds through a fatty area on its forehead known as themelon. Bill Barklow thinks hippos, although they do have vocal cords, may also release sounds into the water through a roll of fat in their throats.

Both may "hear" through their jaws. Ken Norris of the University of California at Santa Cruz examined dolphin skulls to find evidence that sounds are conducted through the lower jaw to the dolphin's ears. Barklow found similar structures in hippos that he believes may make it possible for hippos to listen to sounds above the surface with their ears while simultaneously monitoring underwater sounds through its submerged jaw.

They have a close blood match. Jerold Lowenstein of the University of California at San Francisco has compared blood serum of whales with many ungulates, including cattle, pigs, and gazelles. He found whales were more similar to hippos than to any other group (although DNA studies have not confirmed this). (source: "Snatching Scientific Secrets from the Hippo's Gaping Jaws," David M. Schwartz, Smithsonian,March, 1996)

How do beaked whales feed?

Baleen whales strain plankton through their bristly baleen; toothed whales swallow their prey in huge gulps. Most whales can ingest vast quantities of food through mouths that match their enormous size. Beaked whales, however, have small mouths and little or no teeth, but they still manage to devour squid and fish. How can they gobble up their meals through their dainty mouths?

John Heyning, curator at the Natural History Museum of Los Angeles County, climbed into the tank of a rescued Hubb's beaked whale to find out for himself. He placed his hand over the whale's mouth which sucked it up like a dustball. Beaked whales use suction, as nurse sharks do, to swallow their prey.

Heyning and James Mead, curator of mammals at the National Museum of Natural History, have determined that beaked whales "use their tongues like pistons to suck in their prey."

(source: "Suction Power," National Wildlife,Oct/Nov, 1997)

How do feeding whales keep warm in frigid water?

John Heyning and James Mead have also made a curious discovery about the gray whale's mouth. A gray whale's five-foot-long tongue makes up fully 5% of its body surface area, a significant part of its body to be dragging through icy-cold waters. Slurping up krill in the Arctic Ocean should quickly chill the animal like eating ice cream in winter does to humans. But when the scientists dissected a gray whale tongue they discovered blood vessels clustered around the arteries that carry warm blood from the heart. As the blood circulates, its warmth is passed from the arteries which carry blood from the heart, to the surrounding vessels, which carry blood returning to the heart. These heat-conserving countercurrent exchanges are also found in other whale extremities-fins and flukes.

Do whales sleep?

Some scientists believe that whales "catnap" so that at least part of their brain is aware of what is going on around them. Since whales and dolphins have to breathe consciously (humans are "unconscious" breathers-we breathe even in our sleep), they also have to wake up to take a breath.

Some scientists have postulated that dolphins and whales sleep with half a brain -- half their brain rests while the other half stays alert. Recently, though, other researchers have come to doubt this theory.